Redirection strategies for load sharing in Call Server clusters

A Call Server in a telephone switch is responsible for switching calls between calling and called subscribers. A cluster of Call Servers that serves the subscribers in a large geographical area can provide scalability, reduced operational cost, fault tolerance and load sharing. This paper focuses on strategies for redirecting new calls for load sharing in Call Server clusters. It investigates relative performances of static and adaptive approaches for effectively handling the load spike's occurring on the system. A detailed simulation model is developed using the OPNET tool. The model is used to study the performance of the Call Server clusters using various redirection strategies under different load conditions. A comparison of the performances of these redirection strategies and various insights gained into their behavior and performance are presented. It has been observed that adaptive policies that use load information of the overloaded Call Server and the under loaded Call Server perform better than the static for a wide range of system load